Hydrogenase Sites surprisingly Similar

The structure of the iron-based active site in mononuclear [Fe]-hydrogenase reveals unexpected similarities to iron centers in the binuclear [NiFe]- and [FeFe]-hydrogenases, according to a group of researchers led by Seigo Shima at the Max Planck Institute for Terrestrial Microbiology and Ulrich Ermler at the Max Planck Institute of Biophysics, both in Germany (Science 2008, 321, 572). Hydrogenases catalyze the formation and consumption of H₂ and are of interest commercially as replacements for platinum catalysts that produce H₂ fuel. The crystal structure of [Fe]-hydrogenase indicates there are five ligands to the metal: a cysteine (Cys) sulfur, two CO molecules, the nitrogen of a 2-pyridinol cofactor compound, and a ligand the researchers were unable to identify. A solvent molecule occupies the sixth ligation site, but it is too far away to be considered a ligand. The researchers suggest that the sixth site is where H₂ binds. Notably, although the structures evolved independently, iron sites of the [NiFe]- and [FeFe]-hydrogenases also include a cysteine sulfur, two CO molecules, and a cyanide ligand akin to the 2-pyridinol, making the hydrogenases a remarkable example of convergent evolution, the authors say.